The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The HDA includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The PCBA includes electronics and firmware for controlling the rotation of the spindle motor and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The spindle motor typically includes a rotor including one or more rotor magnets and a rotating hub on which disks are mounted and clamped, and a stator. If more than one disk is mounted on the hub, the disks are typically separated by spacer rings that are mounted on the hub between the disks. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the rotor magnet(s), thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks.
The HSA typically includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. During operation of the disk drive, the actuator must rotate to position the HGAs adjacent desired information tracks on the disk. The actuator includes a pivot-bearing cartridge to facilitate such rotational positioning. The pivot-bearing cartridge fits into a bore in the body of the actuator. One or more actuator arms extend from the actuator body. An actuator coil is supported by the actuator body, and is disposed opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, to form a voice coil motor. The PCBA provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator.
Each HGA includes a head for reading and writing data from and to the disk. In magnetic recording applications, the head typically includes a slider and a magnetic transducer that comprises a writer and a read element. In optical recording applications, the head may include a mirror and an objective lens for focusing laser light on to an adjacent disk surface. The slider is separated from the disk by a gas lubrication film that is typically referred to as an “air bearing.” The term “air bearing” is common because typically the lubricant gas is simply air. However, air bearing sliders have been designed for use in disk drive enclosures that contain helium, because an inert gas may not degrade lubricants and protective carbon films as quickly as does oxygen. Helium may also be used, for example, because it has higher thermal conductivity than air, and therefore may improve disk drive cooling. Also, because the air bearing thickness depends on the gas viscosity and density, the air bearing thickness may be advantageously reduced in helium relative to air (all other conditions being the same). Furthermore, because helium has lower density than air, its flow (e.g. flow that is induced by disk rotation) may not buffet components within the disk drive as much, which may reduce track misregistration and thereby improve track following capability—facilitating higher data storage densities.
Disk drive enclosures disclosed in the art to contain helium are typically hermetically sealed in an attempt to prevent an unacceptable rate of helium leakage. Although some negligible amount of helium leakage is unavoidable, a non-negligible amount of helium leakage is undesirable because it can alter the thickness of the gas lubrication film between the head and the disk, and thereby affect the performance of the head. A non-negligible amount of helium leakage is also undesirable because it can alter the tribochemistry of the head disk interface, possibly leading to degradation in reliability, head crashes, and associated data loss.
Certain disk drives that contain air may include a small opening in the disk drive enclosure to allow a limited flow of air from the outside environment, for example through a labyrinth path and/or a breather filter, to equalize the internal air pressure within the disk drive with the outside air pressure. However, certain other disk drives that contain air may be hermetically sealed, with the disk drive enclosure under some stress to maintain super-ambient or sub-ambient pressure within the disk drive.
Various methods and structures have been disclosed in the past to hermetically seal disk drive enclosures. Some of these have been too costly, have required too much change to existing disk drive manufacturing processes, and/or were not able to retain helium internal to the disk drive enclosure for sufficient time to ensure adequate product reliability. Others have made rework of disk drives (after assembly) difficult or impractical, or had structural problems such as blistering of flexible seals due to gas pressure within the disk drive enclosure being temporarily or permanently super-ambient or sub-ambient.
Thus, there is a need in the art for a disk drive design that may be practically hermetically sealed in a high volume and low cost manufacturing process, and/or that can retain air, helium, or another gas internal to a disk drive enclosure for a sufficient period of time to ensure adequate post-manufacture product reliability and lifetime. There is also a need in the art for a disk drive design that may better resist excessive seal blistering and/or other structural problems that may result from the gas pressure within the disk drive being or becoming different from the gas pressure outside of the disk drive enclosure.